1. Field of the Invention
The present invention relates generally to the field of ophthalmics, more particularly to ophthalmic devices, still more particularly to ophthalmic devices known as intraocular lenses (IOLs), and especially to accommodating intraocular lenses.
2. Background Discussion
At the onset it may helpful to the understanding of the present invention to define the terms “phakic” and “aphakic” as related to human eyes. The term “phakic” is applied to an eye in which the natural ocular lens is still present. This is in contrast to an “aphakic” eye from which the natural ocular lens has—for any reason—been removed. A phakic eye is considered a dynamic or active eye because the living natural lens is subject to change over time, while an aphakic eye is considered a static eye because the natural lens has been removed.
Vision in a normal, healthy eye is enabled by light from a viewed object being refracted to the retina in turn by the cornea and the natural lens located rearwardly of the cornea. An important function of the natural lens, through a process of ciliary muscle contraction and zonular relaxation, is the providing of accommodation, that is, the ability of the elastic natural lens to change its curved shape to enable the eye to focus on objects at distances from near to far in response to the eye and brain sensing an out-of-focus image.
A relatively common ocular problem is impaired or complete loss of vision due to the natural ocular lens becoming cloudy or opaque—a condition known as cataract. The formation of cataracts is typically age related, most individuals over the age of about 60 years suffering from cataracts at least to some extent.
Cataracts cannot currently be cured, reversed, or even significantly arrested. Accordingly, treatment of cataracts involves surgically removing the natural lens when the lens becomes so cloudy that vision is greatly impaired, the result being that a phakic eye becomes an aphakic eye. After a defective natural lens has been surgically removed, the current vision-restoring practice (since about the 1940's) is to implant in the aphakic eye an artificial refractive lens called an intraocular lens (IOL). Previously, thick, heavy, high diopter spectacles were prescribed for aphakic eyes. However, most patients dislike such spectacles because of their uncomfortable weight and unattractive appearance.
Although the implanting of an IOL can generally restore vision in an aphakic eye, corrective spectacles or contact lenses are still usually required for near or far vision, depending upon whether the implanted IOL is selected for far or near vision. This is because, to the knowledge of the present inventor, IOLs providing accommodation comparable to that of a natural healthy lens have not heretofore been available; although, the development of accommodating IOLs has been widely sought.
In addition to the desirability of implanting accommodating IOLs in aphakic eyes in place of the removed natural lens, the implanting of accommodating IOLs would be advantageous in phakic eyes in which the intact natural lens, while still otherwise clear, has lost all or much of its accommodating properties, for example, by becoming less flexible. Nevertheless, the ciliary muscle, which normally functions to provide accommodation of the natural lens generally, remains active for most of an individual's life.
Efforts toward developing accommodating IOLs have relied upon axial IOL movement in the eye and/or IOL lens surface shape change to create dynamic change in ocular power and thus provide accommodation.
Axial movement of implanted IOLs in the eye to provide accommodation is disclosed, for example, in U.S. Pat. Nos. 5,476,514; 5,496,366; 5,674,282 and 6,197,059 to Stuart Cumming. Difficulties associated with axial IOL movement to provide accommodation are due both to the extremely limited ocular space for axial IOL movement that limits the achievable diopter variation necessary for full accommodation, and to satisfactory ocular mechanisms for causing such axial IOL movement.
On the other hand, lens surface shape changing, exemplified in the disclosures of U.S. Pat. Nos. 4,842,601; 4,888,012; 4,932,966; 4,994,082; 5,489,302 have required a spherical lens shape to interact with the rim of ciliary muscle in more then one meridian or even from all 360° orientations. This requires perfect lens centration in regard to the ciliary rim and equal interaction from all meridians; otherwise, absence of central symmetry leads to unequal lens surface curvature in different meridians with resulting reduction in image quality.
Because of these and other problems, a principal objective of the present invention is to provide an improved, surface shape changing accommodating IOL that relies on the interaction with the ciliary muscle in only one meridian. Such improved surface shape changing IOLs may be configured for implanting in aphakic eyes or may alternatively configured for implanting in phakic eyes.